For a number of years power outlets with safety interlocks have been used in shipping yards for providing power to refrigerated devices on shipping docks. In operation, when a pin from a device is inserted into a receptacle of one of these outlets, no power is provided to the device until a safety interlock is deactivated, which enables a circuit break thereby allowing the device to receive power.
Typical power outlets with safety interlocks use one large spring to return both the ground pin and pushrod to their normal positions when a pin is withdrawn from the receptacle. This design makes pin insertion very difficult because of the great force needed to insert a pin that requires forcing a ground pin inward, which is highly tensioned. Still other power outlets use one spring for the ground pin and another spring to serve in pushrod return, but the springs do not work in conjunction to return the pushrod to its normal position when a pin is removed with the circuit breaker activated. Thus, a large spring is required to provide tension on the push rod, making it difficult to push inward to activate the circuit breaker. Typical power outlets also use a complicated system of push rods, levers, pulleys, springs, and cams to provide a safety interlock. These complex designs are labor intensive and do not lend themselves to simple field servicing.
Typical power outlets also do not have a cam stop for providing the safety interlock that prevents the pushrod from actuating the circuit breaker while a pin is uninstalled in the receptacle. Further, because a cam stop is not supplied in current designs, no cam stops are rotated by inward movement of the ground pin when the pin is installed in the receptacle to enable the circuit break to be activated.